388 THE CEREBELLUM. 



at page 386, so that at this place the three ventricles communi- 

 cate with each other. 



From the plexus choroides of each side, where it has 

 passed under the fornix at the anterior angle, a large vein is 

 turned backwards, so as to run nearly over the fissure of the 

 third ventricle towards the pineal gland. Several veins from 

 the surface of the ventricle join this vein near its commence- 

 ment ; thus formed, it passes along with the corresponding 

 vein from the opposite side, sometimes in contact and some- 

 times separated from it a small distance ; near the pineal gland, 

 these veins unite into one trunk, the great internal vein of the 

 brain, called the T-^ena Galeni : which terminates soon after in 

 the torcular Herophili. 



Of the Cerebellum. 



The cerebellum is situated in the lower and posterior part 

 of the cavity of the cranium, in contact with that portion of 

 the OS occipitis which is below the groove for the lateral sinuses. 

 It is, of course, much less than the brain. 



It is covered above by the tentorium, and is divided below 

 into two lobes, by the falx minor. 



The surface of the cerebellum differs in some respects from 

 that of the cerebrum. Instead of the convolutions, there are 

 small superficial depressions, which are nearly horizontal, 

 tending to divide the cerebellum into strata. The pia mater 

 extends into these depressions ; and the tunica arachnoidea 

 passes over them, as in the cerebrum. 



The exterior part of the cerebellum is composed of cine- 

 ritious or cortical, and the interior of medullary matter, as is 

 the case with the cerebrum : but the proportions of these sub- 

 stances in the cerebellum, are the reverse of what they are in 

 the cerebrum. 



If sections be made in the cerebellum, the medullary matter 

 is so arranged that it appears like the stem or trunk of a plant, 

 with ramifications extending from it. This appearance has 

 been called the Arbor vita. 



